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Despite reading all available docs on Flyway website, I still don't understand what is baseline good for. Could somebody explain it in plain English and mention some use cases for this command?
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In Flyway, a baseline is simply an entry in the history table, with a version that tells Flyway the point from which to start all subsequent migrations. The baselining process doesn't create any scripts or other files in the Scripts directory.
Baseline migrations are only used when deploying to new environments. If used in an environment where some Flyway migrations have already been applied, baseline migrations will be ignored. New environments will choose the latest baseline migration as the starting point when you run migrate .
Every time the need to evolve the database arises, whether structure (DDL) or reference data (DML), simply create a new migration with a version number higher than the current one. The next time Flyway starts, it will find it and upgrade the database accordingly.
While both tools are based on Martin Fowler's Evolutionary Database, there are many differences in what these tools offer. Here's where Liquibase and Flyway differ. The bottom line is that Liquibase is more powerful and flexible — covering more database change and deployment use cases than Flyway.
Baselining a database at version V1_0__baseline.sql, for example, instructs Flyway to only apply migration scripts that have been created after V1_0. It does this by inserting a migration entry in the SCHEMA_VERSION table used by Flyway. When you run a migration, available migration scripts will only be applied if their version is higher than the baseline version.
You wish to use Flyway on a production and development database. You create a schema only dump of production. This will be the first migration script applied when you create a new empty database using Flyway.
However, because your existing production and development machines are already on this version, you don't want to apply this initial script. To prevent this, you create a SCHEMA_VERSION table and insert "1_0" into the table to instruct Flyway that the database is already at 1_0. Instead of manually creating this table and inserting a row via SQL, you can run the Flyway baseline command.
Then, a few weeks later, there is another database that you haven't brought onto Flyway, but have still been applying update scripts to (maybe you didn't have time). When you bring this database onto Flyway, you may need to baseline it at V3_0 or some other version.
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